Axial piston unit



May 31, 1966 H. THOMA 3,253,551

AXIAL PISTON UNIT Filed Aug. 16, 1963 5 Sheets-Sheet 1 May 31, 1966 H. THOMA 3,

AXIAL PISTON UNIT Filed Aug. 16, 1963 5 Sheets-Sheet 2 1 13 ,2 n ll' 1 /5- i May 31, 1966 H. THOMA 3,253,551

AXIAL PISTON UNIT Filed Aug. 16; 1963 5 Sheets-Sheet :5

May 31, 1966 H. TH OMA 3,253,551

AXIAL PISTON UNIT Filed Aug. 16, 1963 5 SheetsSheet 4 May 31, 1966 H. THOMA 3,253,551

AXIAL PISTON UNIT Filed Aug. 16, 1963 5 Sheets-Sheet 5 United States Patent .0

3,253,551 AXIAL PISTON UNIT Hans Thoma, Bellevueweg 25, Zug, Switzerland Filed Aug. 16, 1963, Ser. No. 302,515 16 Claims. (Cl. 103-162) This invention relates to hydraulic units of the type in which a rotating cylindrical cylinder block bears at one end against a stationary surface provided with inlet and discharge ports (called a control block) and bores in the cylinder block form cylinders parallel to the axis of rotation, pistons in the cylinders extend from the end of the cylinder block remote from the control block and are operatively connected to a wobble plate so that, as the cylinder block rotates, the pistons are reciprocated in the cylinder bores.

It is necessary to provide means to supply a force to press the cylinder block and the surface of the control block, which latter is provided with inlet and outlet ports, together into sealing engagement. For this purpose it has been usual to provide a separate plate as a control block carrying kidney-shaped control parts for the inlet and outlet of the unit. This usual separate control block is movable to a limited extent so that it bears fiat against the rotating cylinder block even if the cylinder block moves slightly out of line. Such plates have been either spring biased or biased by hydraulic balancing pistons in the control block that press against the casing or housing in which the device is enclosed.

It is a disadvantage of such known devices that the control block being movable, still must be sealed hydraulically at the inlet andoutlet ports of the housing. It is also a disadvantage that the balancing pistons, taking their hydraulic pressure from the device itself, are difficult to arrange to give a uniform distribution of force between the distribution plate and the cylinder block.

It is an object of the present invention to provide means to press the rotating cylinder block of such a hydraulic unit and the control surface of the unit together to give the necessary sealing therebetween, and to provide such means-to-press as a structure that is simple yet gives the necessary distribution of force that eliminates the unbalance of pressures between the cylinder block and contrOl surface that has caused, in previously known devices, uneven wear leading to early failure of the device.

It is a further object of the present invention to pro vide means mounted on a shaft coaxial with the rotatable cylinder block to exert an axial force on said cylinder block to press it against the control surface of the device.

Other and further objects and advantages of the device will become apparent from the following description, taken with the accompanying drawings, in which like characters of reference refer to similar parts, and in which:

FIG. 1 is a fragmentary section of a hydraulic device incorporating the structure of the present invention,

FIG. 2 is a fragmentary section of a hydraulic device incorporating a further embodiment of the present invention,

FIG. 3 is a fragmentary section of a hydraulic dev ce incorporating further structure of the present invention,

3,253,551 Patented May 31, 1966 FIG. 4 is a fragmentary section of a hydraulic device incorporating another structure of the present invention, and

FIG. 5 is a fragmentary section of a hydraulic dev ce incorporating a further embodiment of the present invention.

FIG. 1 shows an embodiment of this invention without the enveloping housing. Numeral 1 designates the rotating cylinder block or barrel of an axial piston unit in which several pump pistons 2 work longitudinally, moving in general parallelism to the axis of the cylinder block or barrel (or they may be somewhat inclined to this axis) when they are set in motion by the rotation of the obliquely adjustable driving or wobble plate 3. For this purpose, connecting rods 4 may be used which are connected through a ball and socket joint to the pistons 2, as shown in dotted lines in FIG. 1. The details of the connection between the pistons and the driving plate is not essential to the present invention.

Pistons 2 will be referred to as pump pistons herein and the cylinders in which pistons 2 operate will be referred to as pump cylinders, even though the device may be used as a motor, to distinguish these pistons from pistons 11, 11 and so forth that are to be described below.

Central shaft 8 is shown as supported by the' driving plate 3'using a ball and socket joint 9. The central shaft 8 is movable longitudinally by ball 9. The longitudinal movement of the central shaft 8 is necessary because this mobility is needed for the transmission of the forces of the balancing piston or pistons arranged on or in the control block remote from the cylinder barrel. The central shaft 8 is either firmly connected with the cylinder barrel 1 or, as in the example of FIG. 1, is supported on the spherical shoulder 10 so that the force exerted by the balancing piston 11, arranged on the control block 30 and acting on the central shaft 8, is transmitted to-the cylinder barrel 1 and, the shoulder 10 forming a ball and socket device, the cylinder barrel will adjust to any possible slight misalignment between the elements.

The driving plate 3 is shown in a neutral position. It is at once apparent that swinging shaft 3a to the right or left in FIG. 1 about the center of the ball and socket 9 will cause driving plate 3 to become a wobble plate.

The arrangement of one or more balancing pistons 11 g or 11' in the control block 30 or, alternatively, in the casing or housing of the unit, and a simple connection for the respective balancing cylinders by the passages 20 and 21 with the main pressure channels D1 and D2, is an important feature of the hydraulic unit of the present invention. Thus, it is possible to arrange the balancing pistons as an annular piston around the central shaft 8, as seen in FIG. 1, or as will be seen below as a plurality of pistons arranged around shaft 8.

Known units generally donot dispose the control ports in the sealing face of the cylinder barrel offset radially inwardly from the prolongations of the cylinder axes toward the axis of rotation of the cylinder block. Instead of control ports disposed radially inwardly, the bores of tine cylinders of known devices are merely extended to the aforementioned sealing surface. Due to the reaction of the hydraulic pressure against the sealing surfaces around these extended cylinder bores, it is not possible to balance their reaction forces in the sealing gap with the forces of a balancing" piston between a control plate and the housing of the device. The result is a high moment causing very heavy edge pressures on the sealing and guiding surfaces andthus causing the destruction of the sealing surfaces when this unit is used for high pressure. Therefore, the radial inward offsetting of the control ports is important for this invention, whose object is to eliminate excessive friction and wear on the sealing surfaces and therefore to avoid any considerable edge pressure on the sealing surfaces.

When the driving plate 3 (FIGS. 1 and 2) is pivoted in one direction about the center of ball and socket joint 9 to place the plane of rotation of drive plate 3 at an angle to the axis of cylinder barrel 1 and drive plate 3 is rotated, one port D2 becomes an intake port and D1 becomes a discharge port (or if plate 3 is pivoted in the other direction D1 becomes the intake and D2 the discharge). The pressure in inlet D2 will be low, the pres sure in outlet D1 will be high.

A bore 20 is provided in control block 30 into which an annular balancing piston element 11 fits. Piston 11 may be sealed against leakage of hydraulic fluid by rings. A passage 21, provided with a ball check valve 21' (FIG. 1) leads from passage D1 to the bore 20 and a similar passage 22 provided with ball valve 22' (FIG. 1) leads from passage D2 to the bore 20. A thrust bearing collar or bearing plate 14 is mounted on the end of shaft 8 to bear against piston balancing 11. One or more passages 111 lead through piston 11 to connect the bore 20 with the face of piston 11 opposite the bearing plate 14 to provide hydraulic fluid as a lubricant between the surfaces of elements 11 and 14 so that shaft 8 can rotate freely. Other types of thrust bearings, such as ball or roller bearings, may of course be used between rotatable shaft 8 and non-rotating piston 11. A pin 27 extending into a hole in piston 11 may be provided to prevent rota tion of piston 11 in bore 20.

A spring 25 resiliently holds cylinder barrel 1 against control block 30 when no pressure is developed in either of passages D1 or D2.

It will be noted that the ports in the cylinder block 1 and in the control block 30 are spaced radially inwardly of the circle in which the cylinders lie. From the fact that these ports are very close to the axis of the device two advantages arise: first, the force tending to separate the cylinder block from the control block is reduced as the area of the ports is reduced, and; second, the force that is developed is as close as possible to the axis of shaft 8 so that the moment arm tending to rotate the cylinder block 1 away from control block 30 is a minimum.

Because of this reduction of the force and reduction of the length of the moment arm, the size and diameter of cylinder 11 may be reduced.

The exemplification of the invention shown in FIG. 2 differs in that a plurality of balancing pistons 11' are provided, each operating in a bore or cylinder in the insert 16 in the control block. These bores or cylinders may, of course, be in the control block itself. Pistons 11 in FIG. 2 each operating in a bore constitute collectively a piston and cylinder means to exert a force axially of shaft 8'. In this figure either passage D1 or D2 may be the discharge or pressure side of the device. Passage 21a extends from passage D1 and passage 22a extends from passage D2 to just below insert 16. In order to distribute the fluid under pressure to pistons 11', grooves 23 extend around the bottom of the insert and/ or of the bore in the control block, so that alternate pistons 11' are subjected to the pressure of the discharge port, whichever of ports D1 or D2 it may be, so they exert upward thrust against thrust disc 14' so the pull on shaft 8 is therefore distributed equally in a circle about shaft 8 among the several alternate balancing pistons 11'. The algebraic sum of the pressures in the inlet and in the discharge is positive at all times, and increases as the discharge pressure increases. Since the algebraic sum of the pressures in D1 and D2 is always positive, there will always be an upward force exerted by pistons 11' on shaft 8 to pull the cylinder block against the control block.

Again a fluid passage is provided through each piston 11' so that the friction surface pressing against the bearing plate 14' is lubricated. In the structure here shown, piston 11 is provided with a ball 12 at the top that engages a socket in slipper 13 so that slipper 13 can adjust itself to press evenly on bearing plate 14'. The specific universal mechanism between the pistons 11' and the slipper or slippers is not a part of the present invention.

The device of FIG. 3 differs from that of FIGS. 1 and 2 in providing shaft 8a extending entirely through the device as the drive shaft (or driven shaft if the device is used as a motor). Wobble plate 3a is of conventional design. A spherical surface 10a is the full equivalent of the similar surfaces 10 and 10' of FIGS. 1 and 2.

Splines 40 on shaft 8a mesh loosely, or at least swingably, with splines 41 on the interior of cylinder block 1a, to provide for a positive drive of the cylinder block 1a by shaft 8a (or vice versa).

The pistons 11a operate through plate 14a to exert a pull on shaft-8a to press cylinder block 1a against control block 30a.

It is possible to arrange the balancing pistons on the lower end of this shaft, as seen in FIG. 4. This may be a single balancing piston or a plurality of pistons 11b, as shown in FIG. 4. The respective cylinders are to be connected at 21b and 22b with the main pressure channels by small tubing or the like (not shown), in the same manner as in FIGS. 1-3. The pistons 11b transmit the forces necessary for balancing the cylinder barrel, to avoid edge pressure on the distributing and sealing surfaces, by exerting a compressive force on the shaft 8b which, in turn, presses the cylinder barrel in FIG. 4 by way of shoulder 10b, instead of exerting a tensile force on shaft 8a as described in detail for the unit shown in FIG. 3.

In FIG. 4, the torque transmission from or to the cen tral shaft 8b is provided for at the upper end of this shaft. Of course there would be no difliculty in providing a connection for torque transmission on the lower end of this shaft, as is shown in FIG. 3, by extending shaft 8b downwardly through the bottom of the element 31.

Since the torque transmission connection may be provided at the lower end of this shaft, as shown in the other figures, it is possible to cut off the central shaft 8 just above the spherical shoulder 10b and provide additional means for the radial guidance of the shaft. This may be provided by a second radial bearing on the balancing cylinder body at 31 in FIG. 4 where, for this arrangement, an extension of the central shaft 8 is necessary in any case for the torque transmission connection. However, since it is also possible to arrange radial hearings on the circumference of the cylinder block or barrel 1b, such a shortened central shaft may be floating too, inasmuch as it is only necessary to retain the shoulder 10b as a sufficient connection for the longitudinal forces.

When the shaft 8b in FIG. 4 is thus cut off near shoulder 10b, the inlet and outlet ports may be moved still closer to the axis of the rotatable cylinder block so that the effect of the present invention is even more effective.

FIG. 5 illustrates other modifications that may be used in connection with the present invention, providing the advantage of the arrangement of the balancing piston (or pistons) on a shaft 8 that is, in a measure, similar to that of FIGS. 1 and 2 but, instead of having merely a ball and socket 9, and having the driving plate 3c be driven, the cylinder block 10 is driven by universal drive 32 that is rotated by shaft T.

There is no axial force exerted by universal joint 32 on the cylinder block except for the weak force exerted by spring 250 which will hold the cylinder block 10 against control block 300 when the device is not in use. The universal joint does not receive any axial force from the cylinder block 10.

The hydraulic device of FIG. 5 has the intake and discharge D2 and D1 lead to trunnions 33. The specific structure of this device, however, except of the mounting of cylinder block 16 on and against control block 300, is known so does not need to be described herein.

Cylinder block 1c is mounted for rotation on a hollow shaft or axial bearing 31 firmly connected to control block 300. The fit between block 1c and hollow shaft 31 permits a limited motion therebetween so that as cylinder block 10 is pulled against control block 30!: by the floating shaft 8c, the cylinder block can adjust to bring the faces of blocks 10 and 300 into tight face-to-face contact.

It will be noted that shaft 8 is supported by spherical surface 10c and by piston 110 at the other, so shaft 80 is a floating shaft. The piston 110 is stepped to provide two concentric piston faces 34 and 35 of equal area. Passages 21c and 22c respectively connect the cylinder spaces c and 20c opposite piston surfaces 34 and 35, respectively, to the discharge D2 and intake D1, respectively.

This arrangement of concentric pistons assures a positive axial pull on floating shaft 8c as the algebraic sum of the pressures in D2 and D1 is positive.

It is seen, therefore, that there is provided in each of the examples described above a means to exert an axial force on a cylinder block that can be tilted a limited amount to accommodate itself to minor angularities between the faces of the cylinder block and the control block. This is done by providing a shaft, to transmit the force, connected to the cylinder block by a ball connection and providing a piston and cylinder means connected by hydraulic passage to the pump discharge, or to the pressure side of the device if used as a motor, to provide the force required to bias the shaft in the direction to press the cylinder block and the control block toward each other.

What is claimed is:

1. A hydraulic unit of the type having a rotary cylinder block, a plurality of pump cylinders in said block generally axially of said block and lying in a circle about the axis of said cylinder block, a piston in each said cylinder, operating means for each said piston extending from one end of said cylinder block, wobble plate means engaging said operating means whereby said pistons may be reciprocated in said cylinders, the end of said rotary cylinder block remote from said operating means being planar, and being provided with ,a combined inlet and outlet port for each cylinder, a control block in face-toface contact with said planar surface of said cylinder block, two ports in said control block, one constituting an inlet port and the other constituting an outlet port, a shaft lying axially of said rotary cylinder block, shoulder means connecting said shaft to said rotary cylinder block so that movement of said shaft axially of itself will urge said rotary cylinder block against said control block, at least two balancing piston and cylinder means having axes parallel to the axis of said rotary cylinder block connected to said shaft, said balancing piston and cylinder means operating, when pressure is supplied thereto, to urge said shaft axially in the direction to press said cylinder block against said control block, to provide fluid pressure to said cylinder and piston means, whereby said cylinder block is pressed against said control block, said wobble plate means being rockable about an axis normal to the axis of said cylinder block so that either of said two ports in said control block may be the outlet port and passage means provided from each of said two ports of said control block to a said piston and cylinder means.

2. The device of claim 1, in which each said passage means includes check valve means to prevent flow from said piston and cylinder means to said passage means.

3. The device of claim 2, in which said balancing piston and cylinder means is mounted in said control block and comprises a cylinder coaxial of said shaft and a piston secured to said shaft.

4. The device of claim 1, in which said balancing piston and cylinder means comprises an even number of cylinders arranged in a circle around the axis of said shaft, each cylinder having a piston means cooperating therewith therein, and the said passage means from said two ports lead to alternate cylinders of said balancing piston and cylinder means, whereby under operating conditions in either direction half of the cylinder and piston means are subjected to hydraulic pressure from the port that is the discharge port.

5. The device of claim 4, in which said balancing cylinder and piston means are mounted on said control block to tension said shaft.

6. The device of claim 4, in which said balancing piston and cylinder means are mounted axially of said cylinder block remote from said control block to place said shaft under compression.

7. The device of claim 1, in which said combined inlet and outlet ports for each pump cylinder are arranged in a circle of less diameter than the circle in which said plurality of pump cylinders lie.

8. A hydraulic device of the type described having an axis, a stationary control block provided with an end face and provided with an inlet and an outlet port spaced radially equally from said axis, a rotatable cylinder block having an'end surface in face-to-face contact with the end face of said control block and provided with a plurality of pump cylinder bores spaced about the axis of rotation of said cylinder block, pump pistons operatively mounted in said pump cylinder bores, passages extending from each said pump cylinder bore to the end face of said cylinder block, said passage lying in a circle so as to pass over said inlet and outlet ports as said cylinder block is rotated, a shaft coaxial with said cylinder block provided with a spherical surface contacting a complementary surface on said cylinder block, balancing piston and cylinder means including a piston body surrounding said shaft, said piston body being formed with two annular surfaces of equal area, and a cylinder of a shape complementary to said piston means and presenting two annular faces opposing the two annular surfaces of said piston, and in which said hydraulic passage means extend from said inlet port to one of the two annular surfaces of said cylinder, and from said outlet port to the other of said two annular surfaces of said cylinder whereby a force is exerted axially on said shaft means to bias said spherical surface of said shaft against the complementary surface of said cylinder block to press said end face of said cylinder block against said control block. Y

9. The device of claim 8 provided with an adjustable wobble plate operatively connected to said pump pistons, and ball and socket support means in said wobble plate engaged by said shaft to support said shaft radially.

10. The device of claim 9, in which said balancing piston and cylinder means comprise a single cylinder coaxial of said shaft and a piston surrounding said shaft, and in which thrust bearing means are provided between said piston and said shaft to transmit a force axially of said shaft.

11. The device of claim 9, in which said balancing piston and cylinder means comprise an even number of pistons, each operating in a separate cylinder, and thrust bearing means are provided between said piston and cylinder means and said shaft to transmit an axial force from said piston and cylinder means to said shaft.

12. The device of claim 8 provided with an adjustable wobble plate, a central aperture in said wobble plate, said shaft extending through said wobble plate and supported by radial bearings near each end of said shaft.

13. The device of claim 12, in which said piston and cylinder means is mounted in said control block.

14. The device of claim 12, in which said piston and cylinder means is operatively mounted on the part of said shaft extending through said wobble plate and remote from said control block.

15. The device of claim 8, in which said shaft is supported solely by said spherical surface and by said balancing piston and cylinder means.

16. The device of claim 15, in which a hollow projecting bearing is provided extending axially from said control block to engage and support said cylinder block against radial movement.

References Cited by the Examiner UNITED STATES PATENTS Vickers 103-162 Ferris 103-162 Bowers et al l03162 Pitt et a1 103--162 Thoma 103-162 Boyer 103162 10 SAMUEL LEVINE, Primary Examiner.

LAURENCE V. EFNER, Examiner. 

1. A HYDRAULIC UNIT OF THE TYPE HAVING A ROTARY CYLINDER BLOCK, A PLRUALITY OF PUMP CYLINDERS IN SAID BLOCK GENERALLY AXIALLY OF SAID BLOCK AND LYING IN A CIRCLE ABOUT THE AXIS OF SAID CYLINDER BLOCK, A PISTON IN EACH SAID CYLINDER, OPERATING MEANS FOR EACH SAID PISTON EXTENDING FROM ONE END OF SAID CYLINDER BLOCK, WOBBLE PLATE MEANS ENGAGING SAID OPERATING MEANS WHEREBY SAID PISTONS MAY BE RECIPROCATED IN SAID CYLINDERS, THE END OF SAID ROTARY CYLINDER BLOCK REMOTE FROM SAID OPERATING MEANS BEING PLANAR, AND BEING PROVIDED WITH A COMBINED INLET AND OUTLET PORT FOR EACH CYLINDER, A CONTROL BLOCK IN FACE-TOFACE CONTACT WITH SAID PANAR SURFACE OF SAID CYLINDER BLOCK, TWO PORTS IN SAID CONTROL BLOCK, ONE CONSTITUTING AN INLET PORT AND THE OTHER CONSTITUTING AN OUTLET PORT, A SHAFT LYING AXIALLY OF SAID ROTARY CYLINDER BLOCK, SHOULDER MEANS CONNECTING SAID SHAFT TO SAID ROTARY CYLINDER BLOCK SO THAT MOVEMENT OF SAID SHAFT AXIALLY OF ITSELF WILL URGE SAID ROTARY CYLINDER BLOCK AGAINST SAID CONTROL BLOCK, AT LEAST TWO BALANCING PISTON AND CYLINDER MEANS HAVING AXES PARALLEL TO THE AXIS OF SAID ROTARY CYLINDER BLOCK CONNECTED TO SAID SHAFT, SAID BALANCING 